Changes in Matter Physical Changes –Altering a substance without changing its composition Cutting up paper Breaking a pencil Crushing rocks Changing states of matter »Ice –melting  liquid »Water –melting  water

Changes in Matter Chemical Changes  –Process where one or more substance changes into a new substance Rusting Fire Reactants- substances that we begin with Products-substances that we end with Reactant  Products

Changes in Matter Evidence of chemical reaction: 1.Gas is produced 2.Color Change 3.Change in smell 4.Formation of solid—precipitate 5.Light is produced 6.Temperature change -exothermic -endothermic

Law of Conservation of Mass Mass is neither created nor destroyed Mass reactants = Mass products Reactants  Products H 2 + O 2  H 2 O 18 g + 22 g  ?g H 2 O

Steps to solve Law of Conservation of Mass problems 1.Write what you know chemical reaction reactants and their masses products and their masses 2.What are you solving for? 3.Solve for your unknown

From a laboratory experiment designed to separate water into hydrogen and oxygen gas, a student collected 10.0 g of hydrogen and 79.4 g of oxygen. How much water was initially involved in the process? Chemical Reaction H 2 O  H 2 + O 2 Reactants  Products What do we know? H 2 = 10.0 g O 2 = 79.4 g What is our unknown? H 2 O = ??? g Law of Conservation of Mass says… Mass reactants = Mass of Products H 2 Omass = H 2 mass + O 2 mass H 2 Omass = 10.0 g g H 2 O mass = 89.4 g

A student carefully placed 15.6 g of sodium in a reactor supplied with an excess quantity of chlorine gas. When the reaction was complete, the student obtained 39.7 g of sodium chloride. How many grams of chlorine gas reacted? Chemical Reaction Reactants  Products Sodium + Chlorine  Sodium Chloride What do we know? Sodium = 15.6 g Sodium Chloride = 39.7 g What is our unknown? Chlorine = ??? g Law of Conservation of Mass says… Mass reactants = Mass of Products Sodium mass + Chlorine mass = Sodium Chloride mass 15.6 grams + ? grams = 39.7 grams ? grams = 24.1 grams of Chlorine

In a flask, 10.3 g of aluminum reacted with 100 g of liquid bromine to form aluminum bromide. After the reaction, no aluminum remained, and 8.5 grams of bromine remained unreacted. How many grams of compound were formed? Chemical Reaction Reactants  ProductsAluminum + Bromine  Aluminum Bromide What do we know? Aluminum = 10.3 g Bromine = 100 g Bromine left over = 8.5 g Bromine used = ?? = 100 – 8.5 g = 91.5 g What is our unknown? Aluminum Bromide = ??? g Law of Conservation of Mass says… Mass reactants = Mass of Products Aluminum used+ Bromine used = Aluminum Bromide made 10.3 grams grams = ??? grams grams = ? Grams of Aluminum Bromide